Growth of high-quality single-crystal gallium nitride (GaN) is essential for optoelectronic and high-power device applications. Native GaN substrates are not commercially available for GaN homoepitaxy, because of the low solubility of nitrogen in bulk gallium (Ga). Thus, GaN-based device structures are currently grown by heteroepitaxy on a variety of foreign substrates, including sapphire, silicon carbide (SiC) or the like. Of the substrates suggested, sapphire remains the most widely used substrate because of its hexagonal symmetry and thermal stability at high temperatures during GaN growth. However, threading dislocations (TDs) and stacking faults generated due to lattice mismatches between sapphire and GaN cause a high density of defects in epitaxial GaN. To reduce the defect density, various techniques of lateral epitaxy (e.g., epitaxial lateral overgrowth (ELOG)) have been suggested. As such, the density of TDs can be reduced to 106 cm−2 or lower. However, such a density value is still much higher than that for gallium arsenide (GaAs) homoepitaxy (102 cm−2 to 104 cm−2).